(5) Making piles too large or too small or careless piling, resulting in any case in serious damage to advance reproduction.

(6) Letting piling get behind logging to such an extent that the slash dries out and is hard to pile and the leaves and twigs fall off. At its best, as illustrated on many national forest cutting areas, piling and burning results in an excellent clean-up of the cut-over

FIG. 23.-POOR SLASH PILING IS EQUIVALENT TO BROADCAST BURNING

With small, loose piles of slash, heaped up without regard for remaining growth, the expense of piling is considerable, and the result is equivalent to a broadcast burn. Reasonable care will prevent this destruction.

lands, with slight damage to reproduction. At its worst, as illustrated particularly on certain private lands where slash has been piled and burned by contract, it approximates broadcast burning in its effect. (Fig. 23.)

ADVANTAGES

Studies on national forest cutting areas where a good job of piling and burning has been done, show that 6 to 17 per cent of the total ground area is covered by the burned slash piles, depending on the density of stand and volume of timber cut. By proper location of the piles in skidding trails and in natural openings, the damage to young growth can be practically eliminated. Scattered as the burned spots are, under the best practice, they offer little more opposition to full timber production than do the loose bowlders found in many thickly forested regions.

The desirability of piling and burning, carefully done, is beyond question. It is the most that can be done under present conditions in reducing inflammable material. Experience shows that fires on cut-over areas where slash has been disposed of are not greatly more difficult to control than in virgin forest, and areas on which slash has been piled and burned have seldom been burned over after logging. On the basis of experience to date, piling and burning, though costing from 40 to 50 cents per thousand feet of lumber, is known to be a success, and deserves the preference over other methods of slash disposal, where maximum yield in second growth is

the owner's aim. Leaving of slash, under intensive patrol, has not yet this recommendation, but is a possible substitute well worthy of further study and test.

Even with piling and burning, systematic fire protection of all lands remains the key to growing timber. Besides piling and burning slash, it will be found desirable to fall snags on all cutting areas. The trifling cost per thousand feet cut is more than repaid by the greater ease and certainty of stopping fires if no snags are present to aid in spreading the fires by spotting.

COST OF SLASH DISPOSAL AND SPECIAL FIRE PROTECTION

The various practices that have been recommended entail direct costs per thousand feet cut, varying from low to high as follows:

Against these costs must be balanced the saving of suppression costs on large fires, which on one large operation amounted to 21 cents per thousand; also the loss of equipment and merchantable stumpage, and loss due to shutdown of operations, the values for which are unknown. Because of the greater productiveness of the lands, systematic reduction of hazard by piling and burning and protection of cut-over lands are good business practice for the owner who is growing timber.

PROTECTION AGAINST INSECTS AND DISEASES

In addition to fire-protection measures, provision should be made for treatment of forest insects and diseases. The methods for controlling tree-killing beetles, particularly those of the genus Dendroctonus, are being worked out by the Bureau of Entomology of the United States Department of Agriculture. Control measures should be used as recommended.

The control of the important wood-destroying fungi and other diseases can, under present economic conditions, best be approached through cutting the diseased trees at the time each area is logged.

If the white pine blister rust becomes established in the sugar pine, special measures will be necessary to prevent serious loss of this most valuable species. Under such circumstances the advice of the forest pathologists of the Bureau of Plant Industry, United States Department of Agriculture, should be the guide.

METHODS OF LOGGING

Damage to advance growth is inevitable in logging the forests in the California pine region; but, as has been seen, the serious loss of seed trees that occurs with high-lead and high-speed logging is not necessary to the profitable exploitation of forests. The measures already discussed aim to preserve at least 50 per cent of the young growth, with the least alteration in existing practices.

The operator engaged in growing timber will be interested in increasing this percentage as much as possible and will desire to minimize logging damage. He can with profit employ measures that have proved valuable on national forest cuttings, in addition to those proposed in the first part of this bulletin.

ADDITIONAL MEASURES TO INSURE BEST TIMBER GROWTH

These additional measures concern chiefly the regulation of donkey yarding. By placing blocks and using shear trees to avoid pulling through areas of established young growth or reserved trees, by placing main lines so that they will not slash around and damage or kill reserved trees, it is possible to increase materially the quantity of reproduction saved. On national forest cuttings where these precautions are exercised in yarding, about 36 per cent of the advance reproduction is destroyed and 7 per cent of the seed trees scarred, but not killed. On private lands the corresponding average losses are 53 per cent and 12 to 20 per cent. The results on national forest cuttings do not involve a material increase in logging cost, and show what can be done if preservation of reproduction is an object.

One other feature of logging requis mention. Lack of care in falling timber ordinarily breaks or injures the crowns of part of the reserved trees, and always destroys a part of the advance. reproduction. It has been estimated by Birch that the extra cost in falling on national forests amounts to only 1 cent per thousand feet cut, and it is only necessary to compare typical national forest and private cuttings to realize that this trifling expenditure means a real difference in the condition of cut-over lands.

The experience of the past decade or more in logging national forest timber shows convincingly that the reduction of damage from various sources is neither impossible nor costly. As the various steps, such as care in felling and in yarding, are actually put into practice, it becomes more and more evident that very slight rearrangement of logging plans and practice makes all the difference between leaving the cut-over land in excellent or in only tolerable condition.

Studies of extra costs of logging national forest stumpage (4) indicate that the cost due to care in yarding and in falling timber to avoid small trees and reproduction amounts to about 7 cents per thousand feet.

The forest owner interested in building up his forest and capitalizing the opportunities for profitable growth will find his constructive effort centered largely on selection of trees to leave. Proper cutting methods, which leave on the ground an adequate number of effective seed trees and thrifty trees capable of rapid growth, constitute the chief factor in making timber growing most profitable. Fire protection, slash disposal, and logging restrictions, important as they are, primarily aim merely to prevent denudation.

ADDITIONAL MEASURES IN CUTTING PRACTICE

The simple cutting measures discussed in the first part of this bulletin do not approach the standard maintained on the national forests. They provide merely for an adequate number of small

seed trees selected mechanically through the device of a diameter limit, supplemented by occasional larger trees. Cutting to a diameter limit does fairly well in obtaining good distribution of trees, but catches some poorly formed, old, and suppressed trees, misses some fine thrifty young individuals, and on part of any cut-over area leaves openings with no trees.

Better practice for producing full timber crops must depend on individual selection of trees to be left. It must, moreover, be based on the same treatment of all species found in virgin forests; and on the selection of reserved trees primarily on the characteristics of the individual trees. Three seed trees per acre, carefully selected, will be at least as effective as four per acre mechanically selected by 'diameter-limit cutting.

The most rapid growth and most effective seeding will be obtained when the reserved trees are selected and marked by a forester or experienced woodsman, familiar both with logging requirements and the characteristics of desirable trees.

SELECTION OF SEED TREES

As already noted, a "seed tree" is a healthy, uninjured tree of over 18 inches diameter; that is, of a size that can be counted on to produce seed immediately after the area has been logged. As size increases cone production per tree also increases, a 26-inch tree producing, on the average, about three times as many cones as an 18-inch tree, though at greater cost in board feet per thousand seeds.

A study in Arizona (10) showed clearly that the germination percentage of seed from blackjack trees was uniformly higher than that from the older yellow pines, and that for trees of the same size the blackjack produced more seed than the yellow pine. Therefore, for seed production, as well as for rapid growth, thrifty young trees should be reserved wherever available.

Where no thrifty young seed trees are present, intermediate trees or, very occasionally, typical mature pines must be kept. Similar conclusions apply to other species, though much less study has been devoted to sugar pine and the firs than to yellow pine.

NUMBER OF SEED TREES REQUIRED

Study of carefully marked national forest cuttings in different types makes it fairly certain, as shown on page 40, that an average of three seed trees per acre, carefully selected, both for their individual characteristics and their distribution, will be sufficient for restocking.

As shown also, the number of young and thrifty trees present is smaller in the East Side yellow pine type than in most other timber types, including the mixtures of yellow and sugar pines, Douglas and white firs, or any two or three of them. On national forest

cuttings, in mixed types, as many as 20 or 25 thrifty young trees per acre are left after cutting, the great majority of which are reserved for growth, not for seed production.

In the great majority of cases thrifty trees selected for growth will serve also as seeders. Only in case no such trees are available on a particular area will it be necesary to reserve trees solely for seeding purposes.

DISTRIBUTION OF SEED TREES

The distribution of seed trees is of fundamental importance. If the production of full timber crops is desired, no mechanical method of selecting the trees or of spacing them is generally applicable.

Obviously the statement that three seed trees per acre are needed does not imply that this number will appear on each acre. The virgin forest is so variable that in following out the principles here laid down it is often necessary to make openings of 2 or even 3 acres in extent, simply because there are no suitable trees to leave. An occasional opening of 3 acres is not to be regarded too seriously, particularly if there are seed trees around the edges. For any extensive area, however, an average of three trees per acre should be left.

SELECTION OF TREES TO LEAVE for groWTH

Full timber-crop production does not stop with the selection of three healthy seed trees to the acre. It demands as well the reservation of other thrifty trees capable of rapid growth after release by cutting. Such trees will be the basis for the second cut, and their selection is the key step distinguishing this type of forest cultivation from the measures previously discussed.

Trees of certain characteristics make rapid growth after release by cutting, and others have no marked capacity for profitable growth. In general, young trees are thrifty; old trees are growing so slowly that though they may respond to cutting the rate of growth is still very low. The external physical marks of youth are; first, the bark, which, particularly in the pine, is dark in color and broken into finer corrugations than on old trees; second, form and shape of crown. Uninjured young trees have conical pointed crowns, the unfailing indication that height growth is in progress. Usually young trees have long crowns, i. e., more than half the total height of the trees. Lumbermen recognize that the young trees, variously called "blackjack" or "bull" pine, yield a poorer quality of lumber than is obtained from the mature or "yellow" pines. Thus, saving young trees for growth and for seeding may not affect seriously the profitability of the logging operation.

Flat or rounded tops, especially the former, are the unfailing indices of old age, and show that height growth has ceased or is at a very low ebb. Cessation of height growth is correlated with great reduction in the rate of diameter growth and with loss of ability to attain a profitable acceleration in growth rate after release. Therefore, the primary rule in selecting trees to leave for growth is to reserve healthy trees of "blackjack "characteristics and to cut "yellow" pines. With the other important species, similar practices should be adopted, cutting the old and leaving the thrifty young

trees.

INCREASED GROWTH ON RESERVED TREES AFTER CUTTING

By careful selection of trees to remain uncut, rapid and profitable formation of wood can be obtained. This is one of the important. sources of value of properly logged lands, and is largely or entirely lost through unregulated logging.

The rate of increase of growth after cutting varies greatly, depending on the amount of cutting close to the trees left, the character of the reserved trees, and the quality of the land.